Pathophysiology of pain in postherpetic neuralgia: a clinical and neurophysiological study.
Postherpetic neuralgia is an exceptionally drug-resistant neuropathic pain. To investigate the pathophysiological mechanisms underlying postherpetic neuralgia we clinically investigated sensory disturbances, pains and itching, with an 11-point numerical rating scale in 41 patients with ophthalmic postherpetic neuralgia. In all the patients we recorded the blink reflex, mediated by non-nociceptive myelinated Abeta-fibers, and trigeminal laser evoked potentials (LEPs) related to nociceptive myelinated Adelta- and unmyelinated C-fiber activation. We also sought possible correlations between clinical sensory disturbances and neurophysiological data. Neurophysiological testing yielded significantly abnormal responses on the affected side compared with the normal side (P<0.001). The blink reflex delay correlated with the intensity of paroxysmal pain, whereas the Adelta- and C-LEP amplitude reduction correlated with the intensity of constant pain (P<0.01). Allodynia correlated with none of the neurophysiological data. Our study shows that postherpetic neuralgia impairs all sensory fiber groups. The neurophysiological-clinical correlations suggest that constant pain arises from a marked loss of nociceptive afferents, whereas paroxysmal pain is related to Abeta-fiber demyelination. These findings might be useful for a better understanding of pain mechanisms in postherpetic neuralgia.
Truini
A
A
Department of Neurological Sciences, La Sapienza University, Viale Università 30, 00185 Rome, Italy Department of Neurological Sciences, IRCCS San Raffaele, Rome, Italy Departments of Anesthesiology and Neurosurgery, Pain Clinic, Helsinki University Hospital, Helsinki, Finland Istituto Dermopatico dell'Immacolata, Rome, Italy Department of Anesthesiology, Tor Vergata University, Rome, Italy.
Galeotti
F
F
Haanpaa
M
M
Zucchi
R
R
Albanesi
A
A
Biasiotta
A
A
Gatti
A
A
Cruccu
G
G
D000368:Aged; D000369:Aged, 80 and over; D001767:Blinking / Q000502:physiology*; D003711:Demyelinating Diseases / Q000473:pathology / Q000503:physiopathology / Q000821:virology; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D006801:Humans; D007834:Lasers; D008297:Male; D008875:Middle Aged; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology; D051474:Neuralgia, Postherpetic / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*; D009482:Neurophysiology / Q000295:instrumentation / Q000379:methods; D009619:Nociceptors / Q000502:physiology; D009882:Ophthalmic Nerve / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods*; D011237:Predictive Value of Tests; D011930:Reaction Time / Q000502:physiology; D020433:Trigeminal Nerve Diseases / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*